Systems, apparatuses and methods for beamforming RFID tags

ABSTRACT

A radio frequency identification (RFID) system includes an RFID interrogator and an RFID tag having a plurality of information sources and a beamforming network. The tag receives electromagnetic radiation from the interrogator. The beamforming network directs the received electromagnetic radiation to a subset of the plurality of information sources. The RFID tag transmits a response to the received electromagnetic radiation, based on the subset of the plurality of information sources to which the received electromagnetic radiation was directed. Method and other embodiments are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/775,871 titled “Systems and Methods for Beamforming RFID Tags,”filed on Mar. 11, 2013, and is incorporated herein in its entirety byreference.

ORIGIN OF THE INVENTION

The invention described herein was made by employees of the UnitedStates government and may be manufactured and used by or for thegovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE DISCLOSURE

The embodiments described herein relate generally to the field of radiofrequency identification (“RFID”). More particularly, the disclosurerelates to systems, apparatuses and methods involving RFID tags thatutilize beamforming.

BACKGROUND

RFID technology may be used, for example, to ascertain the position ofobjects, to track assets, or to assist in navigation. In thistechnology, electromagnetic radiation may be transmitted between an RFIDtag and an RFID interrogator according to any of various arrangements,and the RFID interrogator determines the presence or position of theRFID tag (or the object to which the RFID tag is affixed) by decoding ofinformation contained in the electromagnetic signal received from theRFID tag. With conventional RFID technology, an RFID tag may use eithera wide beam antenna or a narrow fixed beam antenna. Use of a wide beamantenna results in wide distribution of the electromagnetic radiationtransmitted by the RFID tag, or in other words, a wide angular extent ofcoverage, but concomitantly the energy is not focused and consequentlythe range of communication (linear extent or maximum distance withinwhich communication can be conducted) between tag and interrogator islimited. Use of a narrow fixed beam antenna results in a focused beamand hence a long range, but concomitantly is restricted to a narrowangle of coverage such that communication between tag and interrogatoris limited: the tag must be pointed in the direction of the interrogatorin order to communicate with the interrogator; if the interrogator isoff to the side, beyond the angular extent of coverage, the tag andinterrogator cannot communicate. Thus, there is a trade-off betweenlinear extent and angular extent of coverage.

SUMMARY

Embodiments disclosed herein provide systems, methods, and apparatusesfor beamforming RFID tags.

According to a first aspect of the disclosure, a radio frequencyidentification (RFID) system is provided, including an RFID tag. TheRFID tag includes a plurality of information sources and a beamformingnetwork. The RFID tag is configured to receive electromagneticradiation, the beamforming network is configured to direct the receivedelectromagnetic radiation to a subset of the plurality of informationsources, and the RFID tag is configured to transmit a response to thereceived electromagnetic radiation, the response being based on thesubset of the plurality of information sources to which the receivedelectromagnetic radiation was directed.

According to a second aspect of the disclosure, a radio frequencyidentification (RFID) system is provided, including an RFID tag. TheRFID tag includes a plurality of information sources and a beamformingnetwork. The RFID tag is configured to transmit electromagneticradiation via the beamforming network, the electromagnetic radiationencoding one or more identification codes, each identification codeidentifying one of the plurality of information sources, respectively.

According to a third aspect of the disclosure, a radio frequencyidentification (RFID) method is provided. The RFID method includesreceiving electromagnetic radiation, directing the receivedelectromagnetic radiation to a subset of a plurality of informationsources within an RFID tag, and transmitting a response to the receivedelectromagnetic radiation. The response is based on the subset of theplurality of information sources to which the received electromagneticradiation was directed.

According to a fourth aspect of the disclosure, a radio frequencyidentification (RFID) method is provided. The RFID method includestransmitting electromagnetic radiation, the electromagnetic radiationencoding one or more identification codes, each identification codeidentifying a respective one of a plurality of information sourceswithin an RFID tag.

Other aspects and advantages of the embodiments described herein willbecome apparent from the following description and the accompanyingdrawings, illustrating the principles of the embodiments by way ofexample only.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures form part of the present specification and areincluded to further demonstrate certain aspects of the present claimedsubject matter, and should not be used to limit or define the presentclaimed subject matter. The present claimed subject matter may be betterunderstood by reference to one or more of these drawings in combinationwith the description of embodiments presented herein. Consequently, amore complete understanding of the present embodiments and furtherfeatures and advantages thereof may be acquired by referring to thefollowing description taken in conjunction with the accompanyingdrawings, in which like reference numerals may identify like elements,wherein:

FIG. 1 is a schematic diagram, in accordance with one or moreembodiments described herein, of a beamforming RFID tag.

FIG. 2 is a schematic diagram, in accordance with one or moreembodiments described herein, of a terminal port circuit with a radiofrequency (RF) distribution circuit and multiple RFID informationsources.

FIG. 3 is a schematic diagram, in accordance with one or moreembodiments described herein, of a terminal port circuit with aninformation source comprising an integrated circuit and multiplesensors.

FIG. 4 is a schematic diagram, in accordance with one or moreembodiments described herein, of a terminal port circuit with an RFdistribution circuit and multiple RFID information sources attached to awaveguide distribution network.

FIG. 5 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID system, showing transmission ofelectromagnetic radiation from an interrogator to an RFID beamformingtag.

FIG. 6 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID system, showing transmission ofelectromagnetic radiation from an RFID beamforming tag to aninterrogator.

FIG. 7 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID system similar to that of FIG.5, but wherein the electromagnetic radiation is transmitted to the RFIDtag at a different angle corresponding to two terminal ports of the RFIDtag as opposed to a single port as in FIG. 5.

FIG. 8 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID system including multipleinterrogators mounted on respective mobile platforms and a multi-facetedstructure containing an RFID beamforming tag on at least one facetthereof.

FIG. 9 is a schematic diagram, in accordance with one or moreembodiments described herein, of an RFID system including interrogatorsmounted on mobile platforms and a constellation of multiple RFIDbeamforming tags.

FIG. 10 is a schematic diagram, in accordance with one or moreembodiments described herein, of a beamforming network that is a Butlermatrix.

FIG. 11 is a schematic diagram, in accordance with one or moreembodiments described herein, of a beamforming network that is a Rotmanlens.

FIG. 12 is a schematic diagram, in accordance with one or moreembodiments described herein, of a multi-faceted beamforming RFID tag,with a respective single-beam RFID facet-tag attached to each of threefacets of the multi-faceted structure, each of the single-beam RFIDfacet-tags including a single antenna and terminal port.

FIG. 13 is a schematic diagram, in accordance with one or moreembodiments described herein, of a multi-faceted beamforming RFID tag,with a respective beamforming RFID facet-tag attached to each of threefaces of the multi-faceted structure, each of the beamforming RFIDfacet-tags including multiple antennas and multiple terminal ports.

FIG. 14 is a schematic diagram, in accordance with one or moreembodiments described herein, illustrating an exemplary spatial range ofcoverage of beamforming RFID tags.

FIG. 15 is a schematic diagram, in accordance with one or moreembodiments described herein, illustrating an exemplary spatial range ofcoverage of a multi-faceted beamforming RFID tag.

FIG. 16 is a schematic diagram, in accordance with one or moreembodiments described herein, illustrating a hybrid Rotman lens/van Attaretro-reflector.

FIG. 17 is a flow chart, in accordance with one or more embodimentsdescribed herein, of a method of RFID using one or more beamforming RFIDtags.

FIG. 18 is a flow chart, in accordance with one or more embodimentsdescribed herein, of a method of RFID using one or more beamforming RFIDtags.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components and configurations. As oneskilled in the art will appreciate, the same component may be referredto by different names. This document does not intend to distinguishbetween components that differ in name but not function. In thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” The word“or” is used in the inclusive sense (i.e., “and/or”) unless a specificuse to the contrary is explicitly stated.

It should be noted that the terms “radio frequency” (RF) and “microwave”are used interchangeably herein. “Interrogator” and “reader” arelikewise used interchangeably to connote a transceiver that transmitselectromagnetic radiation to one or more RFID tags and receivesresponses from the one or more RFID tags. While the interrogator may beoperationally coupled to one or more processors, such processors may beinternal and/or external to the interrogator. For example, in some casesthe interrogator may have an internal or embedded processor thatcontrols the functionality of the interrogator and is also capable ofdecoding and utilizing information received from one or more tags. Inother cases, the interrogator might have an internal or embeddedprocessor that controls the communication functionality of theinterrogator, and an interface to an external processor enables theexternal processor to utilize information received from the one or moretags.

In the case of surface acoustic wave (SAW) RFID tags, the functionalityof the SAW tag upon the acoustic wave energy, which has been convertedfrom electromagnetic energy by a transducer that imparts information tothat acoustic energy, is an encoding process that is also considered atype of passive modulation. Hence, the terminology “encoding” and“modulation” of the signal with respect to SAW devices is usedinterchangeably, and when used in a general sense, it is understood that“modulation” implies the passive modulation or encoding characteristicof SAW devices.

Although there is not unanimous concurrence regarding the definitionof“waveguides” and “transmission lines,” the consensus opinion is thattransmission lines are a subset of waveguides that propagate,predominantly, transverse electromagnetic (TEM) waves. Herein, the term“transmission line” is used in a more general sense to denote anelongated device for transferring electromagnetic energy between twopieces of equipment, a practice well known to those skilled in the artof electromagnetic engineering (having benefit of this disclosure),regardless of the specific propagation modes established within theelongated device. Although the term “waveguide” sometimes is construedto mean a hollow elongated, usually conductive, tube, the intent in thisdocument is the more general meaning relating to any structure designedto propagate an electromagnetic field in one or more intendeddirections.

The terms “pattern,” “antenna pattern,” “(antenna) radiationdistribution pattern” or the like used herein pertain to the radiationdistribution produced over a solid angular region by injectingelectromagnetic energy within a specific operating frequency band or setof operating frequency bands into one of the terminal ports (describedbelow). The pattern may comprise one or more primary beams, wherein“beam” is used to denote a pattern of radiation density over an angularspan that contains a peak radiation density, and “beam” can also bedescribed as a major lobe. In some embodiments described herein, apattern associated with a terminal port might contain multiple lobes orbeams, each lobe or beam characterized by a local maximum of radiationdensity.

DETAILED DESCRIPTION

The foregoing description of the figures is provided for the convenienceof the reader. It should be understood, however, that the embodimentsare not limited to the precise arrangements and configurations shown inthe figures. Also, the figures are not necessarily drawn to scale, andcertain features may be shown exaggerated in scale or in generalized orschematic form, in the interest of clarity and conciseness. Relatedly,certain features may be omitted in certain figures, and this omissionmay not be explicitly noted in all cases.

While various embodiments are described herein, it should be appreciatedthat the present invention encompasses many inventive concepts that maybe embodied in a wide variety of contexts. The following detaileddescription of exemplary embodiments, read in conjunction with theaccompanying drawings, is merely illustrative and is not to be taken aslimiting the scope of the invention, as it would be impractical toinclude all of the possible embodiments and contexts of the invention inthis disclosure. Upon reading this disclosure, many alternativeembodiments will be apparent to persons of ordinary skill in the art.The scope of the invention is defined by the appended claims andequivalents thereof.

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed or illustrated in this specification. In the development ofany such actual embodiment, numerous implementation-specific decisionsmay need to be made to achieve the design-specific goals, which may varyfrom one implementation to another. It will be appreciated that such adevelopment effort, while possibly complex and time-consuming, wouldnevertheless be a routine undertaking for persons of ordinary skill inthe art having the benefit of this disclosure.

Embodiments disclosed herein may provide certain advantages andbenefits, such as described as follows. The beamforming RFID tagsdescribed herein may permit links (communication) between interrogatorsand tags over longer distances at a fixed interrogator transmissionpower, or over the same distance at a lesser interrogator transmissionpower, than is typically feasible in conventional RFID communicationlinks. Thus, the beamforming RFID tags may permit tracking of assetsover greater distances. Navigation or localization applications are alsopossible due to the multiple, angle-dependent beams associated with thebeamforming RFID tags. Long range wireless sensor interrogationapplications are also possible when the tag incorporates one or moresensing mechanisms.

More specifically, the beamforming RFID tags described herein mayprovide antenna directivity that far surpasses typical values associatedwith RFID tag antennas. The beamforming RFID tags described herein mayalso provide retro-directive functionality, which simulates automatedpassive steering, such that the signal received from the interrogator isfocused on a specific RFID tag and retransmitted back in the directionof the interrogator. Accordingly, the beamforming RFID tags describedherein may be referred to as beamformer RFID retro-reflector tags. Inaddition to the range information associated with typical RFID links,bearing information may also be provided to the interrogator, based onthe identification information in the signal that is reflected back tothe interrogator. That is, the beamforming RFID tag may have the abilityto associate a unique identification code to each beam port, so that theidentification code contained in the response signal transmitted by thetag indicates the angle of transmission. This provision of bearinginformation permits enhanced navigation functionality; e.g., road signsthat return bearing estimation in addition to the typically providedrange and possibly range-rate. Further, the beamformer (or beamformingnetwork) in the beamforming RFID tags described herein may spatiallycondense the power of the incoming electromagnetic radiation (signal) toessentially a point that may be referred to as a beam port (or terminalport). The condensing of power at the beam port makes this RFIDretro-reflector technology suitable for use not only with surfaceacoustic wave circuits but also with integrated circuit-based RFID tags,which require a minimum threshold voltage at the integrated circuitbecause the integrated circuit is powered by the rectified field. Theincreased power permits longer communication links.

A general description of some embodiments disclosed herein is givenimmediately below, followed by a description of embodiments withreference to the figures herein.

Methods, apparatuses, and systems for long-range RFID-enabledcommunication, tracking and other functions, using beamforming RFIDtags, are disclosed, including an RFID system comprising (i) aninterrogator operationally connected to a processor and (ii) one or morebeamforming RFID tags. Each of the beamforming RFID tags comprises oneor more antennas (e.g., an antenna array), one or more terminal portcircuits, and a beamforming network. The beam forming network comprisesone or more antenna ports connecting to the one or more antennas and oneor more terminal ports connecting to the one or more terminal portcircuits. Each of the terminal port circuits comprises one or more RFIDinformation sources. In some embodiments, the information sources areRFID integrated circuits that are powered by rectifying incidentelectromagnetic energy. In some embodiments, the information sources aresurface acoustic wave (SAW) circuits that receive RF energy and transmitencoded RF pulses that are received by the interrogator and decoded bythe processor to derive the identification of the one or moreinformation sources responding. The responding terminal port circuits,and the information sources associated with the responding terminal portcircuits, are determined by (i) the angle of incidence of theelectromagnetic wave impinging on the antennas, relative to a coordinatereference system defined in terms of the antennas' positions andorientations, and (ii) the design of the beamforming network. Thebeamforming RFID tags are characterized by a fixed characteristic set ofantenna radiation distribution patterns (e.g., beams), each suchradiation distribution pattern being associated with one or more of theterminal ports of the beamforming network, and each radiationdistribution pattern determined by the location of the antennasconnected to the beamforming network and by the design of thebeamforming network. In some embodiments, the beamforming RFID tags areable to receive more power by using multiple antennas to achieve ahigher effective directivity.

In an embodiment, the terminal port circuits include sensors attached toone or more of the RFID information sources so that the processor of theRFID system receives sensor telemetry in addition to the identificationinformation associated with the information source. In anotherembodiment, the RFID information sources are inherently integrated witha sensor modality, such as SAW circuits for which temperature telemetry,in addition to the identification code, is derived by the processor ofthe RFID system.

In some embodiments, the beamforming network is a Rotman lens. In someembodiments the beamforming network is a Ghent lens. In someembodiments, the beamforming network comprises RF dividers andcombiners. In some embodiments, the beamforming network is a matrix oftransmission lines and hybrid couplers. In some embodiments, the matrixof transmission lines and couplers is a Butler matrix. In someembodiments, a matrix of transmission lines and directional couplersforms a Blass beamforming network.

In some embodiments, a multi-faceted structure supports a beamformingRFID tag on each face, and the beamforming RFID tag on each faceprovides antenna coverage over a predetermined angular span such thatthe collective beamforming RFID tags over the multi-faceted structureprovide coverage over a predetermined angular span that exceeds the spanof the composite of the single antenna beams associated with a singleface.

In some embodiments, a beamforming RFID tag is formed from amulti-faceted structure in which each face supports a fixed beam antennawith an associated antenna beam, each fixed beam antenna being connectedto an RFID information source such that the multiple antenna beamsassociated with multiple faces provide coverage over a predeterminedangular span that exceeds the span of any of the single antenna beamsassociated with a single face.

In some embodiments, the processor operationally connected to theinterrogator is configured to estimate the angle of the RFID tag antennaarray relative to the direction in which the interrogator istransmitting based on the identification of the responding informationsources. In some embodiments, a constellation of one or more beamformingRFID tags are arranged and surveyed so that the position and orientationof each is known. A mobile platform with an RFID system radiates RFsignals to the one or more beamforming RFID tags and the processoroperationally connected to the interrogator is configured to estimatethe position and/or orientation of the mobile platform based on theidentification of the information sources responding from theconstellation of one or more beamforming RFID tags.

In some embodiments of the beamforming RFID tag, the information sourcesattached to the terminal ports of the beamforming network are batterypowered transmitters that send out RF pulses, and each informationsource is transmitted through one or more beams, each beam covering aspecified angular region according to the beamformer design. In someembodiments, the battery powered transmitters are ultra-wideband (UWB)transmitters. In some embodiments, sensors are attached to one or moreof the information sources so that the transmitted information over themultitude of beams contains sensor telemetry in addition to theidentification associated with the information source.

FIG. 1 depicts one or more embodiments described herein as a beamformingRFID tag 100 comprising multiple antennas 101 (four shown), abeamforming network 102 with multiple antenna ports 107 (four shown) andmultiple terminal ports 103 (five shown), and multiple terminal portcircuits 110, 111, 112, 113 and 114. Antenna ports 107 couple antennas101 to beamforming network 102, and terminal ports 103 couple terminalport circuits 110, 111, 112, 113 and 114 to beamforming network 102. Thenumbers of antennas 101, antenna ports 107, terminal ports 103 andterminal port circuits 110-114 may vary from the numbers illustrated inFIG. 1, the numbers of each of these elements may be two or more, thenumber of antennas 101 may match the number of antenna ports 107, andthe number of terminal ports 103 may match the number of terminal portcircuits 110-114.

The beamforming RFID tag 100 may be said to have a (fixed)characteristic set of antenna radiation distribution patterns,illustrated in FIG. 1 in a simplified manner in the form of single beamsor major lobes 120, 121, 122, 123 and 124. In some embodiments, RFID tag100 may have antenna radiation distribution patterns of types differentfrom those illustrated in FIG. 1. The antennas 101 may receiveelectromagnetic radiation, e.g., an RF signal 130 that has beentransmitted by an RFID interrogator (not shown) at a given angle ofincidence 109 relative to a fixed coordinate system or frame ofreference defined by the position and orientation of the antennas 101,such as Cartesian coordinate system 108 defined by an x-axis and ay-axis intersecting at origin O (0,0). The antennas 101 may transfer thereceived signal 130 via the multiple antenna ports 107 to beamformingnetwork 102. Beamforming network 102 may focus the power (direct thereceived electromagnetic radiation) to a selected one or more of theterminal ports 103 (and hence to a selected one or more of thecorresponding terminal port circuits 110-114 and correspondinginformation sources contained therein, described below), in accordancewith the angle of incidence 109 of the signal 130 relative to the arrayof antennas 101. While the selected one or more of the terminal ports103/terminal port circuits 110-114/information sources may be referredto as a “subset” of the terminal ports 103/terminal port circuits110-114/information sources, it is to be understood that such subset maybe either a proper subset, or an improper subset including the entireset of the terminal ports 103/terminal port circuits 110-114/informationsources. If the angle of incidence 109 is aligned well with a single oneof the characteristic antenna radiation distribution patterns, or beams,120-124 of the beamforming RFID tag 100, then according to at least oneembodiment the signal 130 power is directed predominantly to the one ofthe terminal port circuits 110-114 that corresponds to the single(aligned) one of the beams 120-124. If the angle of incidence 109 of thesignal 130 is within two or more of the beams 120-124 of the beamformingRFID tag 100, then according to at least one embodiment, the signal 130power is distributed between the two or more of terminal port circuits110-114 that correspond to the two or more of the beams 120-124. It isnoted there is not necessarily a fixed mapping between a given one ofthe beams 120-124 of the characteristic antenna radiation distributionset and a given one of the terminal port circuits 110-114, or a uniquemapping between the beams 120-124 and the terminal port circuits110-114. However, in many embodiments, the beamforming network 102 isdesigned such that each of the major beams 120-124 of the characteristicantenna radiation distribution set is associated with only one of theterminal port circuits 110-114 (and hence with the correspondinginformation source contained therein), where “associated” means thatenergy received over that beam is predominantly directed to the oneassociated port, and by reciprocity of the beamforming network 102 andthe array of antennas 101, electromagnetic energy transmitted into thatport is radiated predominantly through only the one associated beam ofthe characteristic set of antenna radiation distribution patterns. It isfurther noted that, while beamforming network 102 may focus or directthe received electromagnetic radiation to a selected one or moreterminal ports 103/terminal port circuits 110-114/information sources,it may occur that (some of) the non-selected, or non-preferred, one(s)of the terminal ports 103/terminal port circuits 110-114/informationsources also receive sufficient signal power to permit response to theinterrogator due to the well-known fact that the directivity or focusingquality of beamforming networks is finite, as well as to unintendedscattering that occurs in beamforming networks. The likelihood ofoccurrences of non-selected, or non-preferred, terminal ports103/terminal port circuits 110-114/information sources receivingsufficient signal power to permit response to the interrogator is likelyto increase in situations in which the RF link is exceptionally strong,such as when the range between the interrogator and tag is very close orwhen the interrogator is transmitting a much higher level of power thanis needed to permit communication with only the selected, or preferred,terminal ports 103/terminal port circuits 110-114/information sources.

Each one of the terminal port circuits 110-114 includes an informationsource (illustrated in FIGS. 2-4) that, after receiving an incidentsignal (i.e., a signal directed thereto by the beamforming network 102),transmits a modulated or encoded form of the incident signal back intothe beamforming network 102, the modulated or encoded signal containinginformation. Due to reciprocity, the beamforming network 102redistributes the encoded or modulated signal power back to the antennas101 with relative time delays such that the signal is transmitted backat the angle of incidence (at which the signal was initially received)and in the direction opposite the direction from which the signalinitially arrived at the RFID tag 100, that is, in the approximatedirection of the interrogator that initially sent the signal to the RFIDtag 100. (The “direction from which the signal initially arrived at theRFID tag 100” may be thought of in terms of a vector oriented at theangle of incidence and directed away from the interrogator and towardthe tag (compare signal 235 in FIG. 5, discussed below) and “thedirection opposite the direction from which the signal initially arrivedat the RFID tag 100” may be thought of in terms of a vector oriented atthe same angle and directed away from the tag and toward theinterrogator (compare signal 236 in FIG. 6, discussed below). In thisregard, the response from each one of the terminal port circuits 110-114is radiated back to the interrogator according to the fixed antennaradiation distribution pattern associated with the respective one of theterminal port circuits 110-114. The interrogator may then receive thisresponse signal (electromagnetic radiation) that has been transmittedback to the interrogator by the RFID tag 100. Each information sourcemay include an identification code. In at least one embodiment, eachinformation source is an RFID integrated circuit capable of respondingwith such identification code identifying the particular informationsource (i.e., capable of encoding the response signal with suchidentification code). In at least one embodiment, each informationsource includes an RFID integrated circuit and a sensor and is capableof responding (i.e., encoding the response signal) with such anidentification code and sensor telemetry. In at least one embodiment,each information source includes a SAW RFID tag (inherently integratedwith a sensor modality) that encodes the response signal with such anidentification code and, optionally, sensor telemetry. The interrogatormay be associated with a mapping between the identification codes of theinformation sources and angles at which the responses are transmitted bythe RFID tag. The interrogator may also be associated with logic forderiving, from the response signal, information pertaining to a positionand/or an orientation of the interrogator and/or tag, as described infuller detail below.

As will be understood from the above, the particular information sources(or particular terminal port circuits 110-114) to which a given incomingsignal 130 (signal 130 arriving at the tag 100) is directed by thebeamforming network 102 may be determined by (selected in accordancewith) the angle of incidence 109 of the incoming signal 130. Also, theinformation sources to which a given incoming signal 130 is directed maybe the information sources that respond to the incoming signal, sendinga response to the incoming signal 130 back to the interrogator. Thus,the particular information sources that respond to the incoming signal130 may also be determined by (selected in accordance with) the angle ofincidence 109 of the incoming signal 130. Thus, the response signalreceived by the interrogator from the RFID tag may include (i.e., beencoded with) one or more identification codes identifying theparticular information source(s) to which the initial signal(transmitted by the interrogator to the RFID tag 100) was directed andfrom which the response (from tag 100 to interrogator) was transmitted.In this sense the response signal may be based on the particularinformation sources to which the received signal was directed by thebeamforming network 102. As will be understood, the response signal maydepend on the angle of incidence 109 of the incoming signal and on thedesign of the beamforming network 102.

The design of beamforming networks will now be described. Typically, abeamforming network is designed to implement, in conjunction withattached antennas, a fixed set of characteristic beams such as beams120, 121, 122, 123 and 124, which in FIG. 1 are shown superimposed uponCartesian coordinate system 108. The set of characteristic beams, orradiation distribution pattern, is determined by the design of theantennas, the locations of the antennas 101, and the design of thebeamforming network 102. As noted, FIG. 1 is schematic, and thoseskilled in the art now having benefit of this disclosure will understandthat in reality beam patterns may have additional side lobes, forexample. Moreover, in at least one embodiment, the beamformer 102 andthe spacing between antennas 101 are designed such that the antennaradiation distribution pattern associated with one or more of theterminal ports 103/terminal port circuits 110-114 exhibits multiple mainlobes or beams, such as are commonly referred to as grating lobes in theart of antenna arrays. In at least one embodiment, the antennas 101 arecollinear, although this need not (but may) be the case in otherembodiments. Each of the terminal ports 103 (and corresponding terminalport circuit and information source) may be associated with one or moreof the characteristic beams 120-124. In this disclosure, the associationof terminal ports 103 and beams 120-124 is intended to imply that an RFexcitation at a specific terminal port 103 produces radiationpredominantly through the one or more associated ones of thecharacteristic beams 120-124. For example, in one embodiment consistentwith FIG. 1, terminal port circuit 110 (and corresponding informationsource) may be associated uniquely with characteristic beam 120,terminal port circuit 111 (and corresponding information source) may beassociated uniquely with beam 121, terminal port circuit 112 (andcorresponding information source) may be associated uniquely with beam122, terminal port circuit 113 (and corresponding information source)may be associated uniquely with beam 123, and terminal port circuit 114(and corresponding information source) may be associated uniquely withbeam 124. (It is noted that in such one-to-one association ofcharacteristic beams with terminal port circuits, the pairing of thecharacteristic beams and the terminal port circuits need not accord withtheir left-to-right or right-to-left ordering, e.g., beam 120 could beassociated with a terminal port circuit other than 110, etc.) Sincereciprocity applies to this passive beamforming network 102 and theattached antennas 101, radiation received in a specific direction willresult in the beamforming network 102 directing the received powertoward the particular ones of the terminal ports 103 that are associatedwith the one or more of the beams 120-124 that are directed in thatspecific direction. The design of the characteristic beam set of thebeamforming network 102 permits infinite degrees of freedom with respectto the primary direction and spacing of the beams 120-124, in additionto infinite degrees of freedom with respect to the coupling of the beams120-124 to specific ones of the terminal ports 103/terminal portcircuits 110-114, and with respect to the number of beams and antennaports. Such functionality of beamforming networks is well known to thoseskilled in the art now having benefit of this disclosure.

As also seen in FIG. 1, beam overlap can vary. For example, beam 122 isdepicted as having less overlap with beams 121 and 123 as compared tothe overlap between beams 120 and 121 and to the overlap between beams123 and 124. In at least one embodiment, the beamforming network 102 isdesigned such that the beams overlap sufficiently that the beamformingRFID tag 100 is capable of communicating with an interrogator over theentire range of angles covered by the characteristic beam set. In FIG.1, this range would include the entire span from the beam center of beam120 to the beam center of beam 124, through all the beams between beams120 and 124, in addition to the spans from the beam centers of beams 120and 124 to the respective limiting angles on the outside of beams 120and 124, where “limiting angle” is defined as the angle at which theminimum antenna gain required to permit the communication link betweenthe interrogator and the beamforming RFID tag 100 is obtained. (The term“limiting angle” need not be restricted in use to beams at the extremesof a set of beams, but may be applied to other beams, for example, inthe case of beams that do not sufficiently overlap to provide forcontinuous coverage.) It is noted that the “limiting angle” is dependentupon several parameters of the link between the interrogator and the tag100, including but not limited to the transmit power of the interrogatorand the propagation environment surrounding the interrogator and the tag100. When an incident signal arrives at an angle at which two beamsintersect, within (inside) the limiting angles of both beams, theterminal ports 103 associated with both beams may receive the incomingpower, and likewise the signal returned from both terminal ports 103 maybe reradiated at substantially the same angle on the same two beams. Itshould be noted that the overlap of beams and the distribution ofincoming power to more than one terminal port, and hence to more thanone information source, does not necessarily lead to simultaneoustransmission from each of the receiving terminal ports and informationsources. In fact, in at least one embodiment, the information sourcescomprise RFID integrated circuits that avoid tag collisions(interference between simultaneous tag transmissions) through timing oftag responses dictated by a communication protocol such as the EPCglobalClass 1 Generation 2 UHF protocol. In such a protocol, the RFIDintegrated circuits may be singulated through a protocol known as an“Aloha” procedure in which only one tag responds at a time.

It will readily be recognized by those skilled in the art of beamformingnetworks, now having benefit of this disclosure, that there are a numberof types of beamforming networks that could be used to implement abeamforming network 102 for application as described herein for abeamforming RFID tag 100. For example, in at least one embodiment, thebeamforming network 102 could be a microwave lens. The design of themicrowave lens could be any of a number of well known microwave lensdesigns. For example, in at least one embodiment the microwave lenscould be a Rotman lens, as described, for example, in “Wide AngleMicrowave Lens for Line Source Applications” by W. Rotman and R. Turner(IEEE Transactions on Antennas and Propagation, vol. 11, issue 6, 1963,pp. 623-632) or in Phased Array Antennas by A. K. Bhattacharyya(Wiley-Interscience, ISBN-13: 978-0-471-72757-6, 2006, pp. 379-415), orany of the microwave lens designs derivative of the Rotman lens, asdescribed, for example, in the aforementioned Phased Array Antennas (pp.379-415), in “Procedure for correct refocusing of the Rotman lensaccording to Snell's law” by D. R. Gagnon (IEEE Transactions on Antennasand Propagation, vol. 37, March 1989, pp. 390-392), or in “Comparison ofthe Performance of the Rotman Type Lenses Obtained by Different DesignApproaches” by P. K. Singhal and R. D. Gupta (TENCON 99, Proceedings ofthe IEEE Region 10 Conference, vol. 1, 1999, pp. 738-741). In at leastone embodiment, the microwave lens could be a lens following designprocedures outlined in the aforementioned Phased Array Antennas (pp.379-415) or the aforementioned “Procedure for correct refocusing of theRotman lens according to Snell's law” (pp. 390-392). In at least oneembodiment, the lens could be a derivative of the Rotman lens such thatthe antenna ports and beam ports are interspersed around a circularregion to create a beamforming network capable of providing coverageover 360 degrees, as described in the aforementioned “Comparison of thePerformance of the Rotman Type Lenses Obtained by Different DesignApproaches” (pp. 738-741). In at least one embodiment, the microwavelens could be a Luneberg lens, or a derivative thereof, as described in“Fan-Beam Millimeter-Wave Antenna Design Based on the CylindricalLuneberg Lens” by X. Wu and J. Lauren (IEEE Transactions on Antennas andPropagation, vol. 55, no. 8, August 2007, pp. 2147-2156). In at leastone embodiment, the beamforming network could be formed from powerdividers/combiners, waveguides, and phase shifters, or the beamformingnetwork could be a derivative of such a beamforming network. In at leastone embodiment the beamforming network could be formed from hybridcouplers, waveguides, and phase shifters, or the beamforming networkcould be a derivative of such a beamforming network. In at least oneembodiment, the beamforming network could be a Butler matrix, asdescribed in the aforementioned Phased Array Antennas (pp. 379-415), ora derivative thereof. In at least one embodiment, the beamformingnetwork could be a Blass matrix, as described in the aforementionedPhased Array Antennas (pp. 379-415), or a derivative thereof. In atleast one embodiment, the beamforming network could be a Ghent lens, ora derivative thereof, as described in British Provisional PatentSpecification No. 25926/56 (“Improvements in or Relating toElectromagnetic-Wave Lens and Mirror Systems,” S. S. D. Jones, H. Ghent,and A. A. L. Browne, August, 1956). All of the documents cited in thisparagraph are hereby incorporated herein by reference.

It is further recognized by and familiar to those skilled in the art,now having benefit of this disclosure, that the selection of thebeamforming network might impose certain constraints. For example, aButler matrix is more easily implemented if the number of antenna portsis 2 to the power m, where m is a positive integer. The Butler matrixcan also be designed such that the beams are orthogonal, as is wellknown in the art, as described in the aforementioned Phased ArrayAntennas (pp. 379-415). It should be noted that the example shown inFIG. 1 is one of many possible beamforming RFID tag implementations, andthat certain selections of beamforming networks might impose constraintsthat might not be consistent with the operation or number or placementof beams and ports as shown in FIG. 1. For example, beamforming networkscreated as a Butler matrix, as described in the aforementioned PhasedArray Antennas (pp. 379-415), are readily implemented with an evennumber of antenna ports and terminal ports, although otherconfigurations are possible.

Terminal port circuits 110-114 may be of varying types, some of whichare illustrated in FIGS. 2-4, description of which is provided after thegeneral description immediately following. Each one of terminal portcircuits 110-114 may include an RF interface (terminal port circuitinterface) to the corresponding terminal port, and an RF distributioncircuit connected to the RF interface and also connected to one or moreinformation sources. The RF distribution circuit may be, for example, anRF power divider or a distributed waveguide. The information sources mayinclude RFID integrated circuits or SAW circuits and may include one ormore sensors of one or more types. The RFID integrated circuit may beattached to the RF interface and include an on-board memory. The RFIDintegrated circuit may be attached to a data acquisition unit, with oneor more sensors attached to a data acquisition unit. In this case, thedata acquisition unit may sample one or more of the attached sensors andprovide the sensor sample and unique sensor source identification to theRFID integrated circuit, and the RFID integrated circuit may store eachsensor sample and unique sensor source identification on the on-boardmemory, and the RFID integrated circuit may communicate with theinterrogator to provide each sensor sample and associated sensoridentification number to a processor connected to the interrogator. TheRFID integrated circuit may be powered by rectifying the RF signaltransmitted by the interrogator. The RFID integrated circuit may becompliant with one or more of the EPCglobal RFID standards. In someembodiments, all the terminal port circuits 110-114 may be the same suchthat the signal transmitted by the tag is characterized by a singleidentification code.

In some embodiments the information sources include RFID integratedcircuits. In other embodiments, the information sources include SAWcircuits. In still other embodiments, some information sources includeRFID integrated circuits and others include SAW circuits. Theinformation sources may also include one or more sensors of one or moretypes (e.g., modalities). The information sources may be powered by abattery and capable of responding to an interrogation signal. Theinformation sources may periodically transmit a signal containing aunique identification. Such signal may include sensor telemetry. Suchperiodic transmission may occur in the absence of any signal transmittedby an interrogator to the tag.

One type of the terminal port circuits 110-114 is shown in FIG. 2according to at least one embodiment. Although the terminal port circuitillustrated in FIG. 2 is assigned reference numeral 110 a, it may bethought of as representative of any or all of the terminal port circuits110-114 in RFID tag 100, as all of the terminal port circuits 110-114may (but need not) be of the same type. Terminal port circuit 110 a is aparallel RF terminal port circuit. Terminal port circuit 110 a isconnected to a terminal port 103 (shown in FIG. 1) of beamformingnetwork 102 (shown in FIG. 1) via terminal port circuit interface 104.Terminal port circuit 110 a includes element 115 a, which may be an RFpower divider (or divider/combiner) or a hybrid coupler, and multipleinformation sources 116. A signal (referred to herein also as an“incident signal”) received by terminal port circuit 110 a frombeamforming network 102 via terminal port circuit interface 104 isdistributed through RF power divider or hybrid coupler 115 a toinformation sources 116. Each information source 116 includes at leastone RFID source (not shown), such as an RFID integrated circuit or a SAWcircuit, and, in some embodiments, one or more sensors (not shown).According to at least one embodiment, each information source 116directs an encoded or modulated form of the incident signal back to theterminal port circuit interface 104 for transmission into thebeamforming network 102 and back to the interrogator through theantennas 101 (shown in FIG. 1) attached to the beamforming network 102.In some embodiments, only one information source 116 responds at anygiven time, and the sequence of responses may be governed by theinterrogator. For example, as mentioned above, in the EPCglobal Class 1Generation 2 protocol, compliant tag RFID integrated circuits onlyrespond in turn as governed by the protocol. The encoded or modulatedsignal is encoded or modulated with information that includes theidentification code or information associated with the informationsource 116, and, in some embodiments, also sensor telemetry. Althoughterminal port circuit 110 a is shown in FIG. 2 with an RF powerdivider/combiner or RF coupler 115 a that distributes power four ways,in other embodiments the coupling factor could be two or three or itcould be more than four.

Continuing to refer to FIG. 2, as discussed above, in some embodimentsthe information sources 116 include RFID integrated circuits, in otherembodiments the information sources 116 include SAW circuits, and instill other embodiments some information sources 116 include RFIDintegrated circuits and others include SAW circuits. Information sources116 may also include one or more sensors of various types (e.g.,modalities).

Terminal port circuit 110 a shown in FIG. 2 represents one exemplarytype of terminal port circuits 110-114 of FIG. 1. FIG. 3 depictsterminal port circuit 110 b, which represents an alternative exemplarytype of terminal port circuits 110-114 of FIG. 1, according to at leastone embodiment. As with terminal port circuit 110 a, terminal portcircuit 110 b is considered representative of any or all of the terminalport circuits 110-114 in RFID tag 100. Terminal port circuit 110 b isconnected to a terminal port 103 (shown in FIG. 1) of beamformingnetwork 102 (shown in FIG. 1) via terminal port circuit interface 104.Terminal port circuit 110 b includes an RFID integrated circuitcommunications section 117 coupled to a data acquisition section 118,which in turn is coupled to one or more information sources 116. Eachinformation source 116 may include an RFID integrated circuit and asensor. According to at least one embodiment, the RFID integratedcircuit communicates with the interrogator (not shown) by alternatelybackscattering and receiving the incident signal in order to return amodulated signal, as is well established in many forms of passive RFIDtag interrogation. In some embodiments, the RFID integrated circuitcommunications section 117 is powered by rectifying all or a portion ofthe incident RF signal, and the same rectified RF power is also used topower the data acquisition section 118 and the sensors. In someembodiments, the rectified power is used to sustain only the function ofthe integrated circuit communications section 117, and the dataacquisition 118 and sensors are powered independently by a battery orother power source. In some embodiments, terminal port circuit 110 b maybe implemented as a single system on a chip (SoC) and deemed an RFID IC.In some embodiments, RFID communications section 117 may constitute anRFID IC and information source 116 may contain a sensor.

Further to terminal port circuits 110 a and 100 b of FIGS. 2 and 3,respectively, FIG. 4 depicts terminal port circuit 110 c, whichrepresents another alternative exemplary type of terminal port circuits110-114 of FIG. 1, according to at least one embodiment. As withterminal port circuits 110 a and 110 b, terminal port circuit 110 c isrepresentative of any or all of the terminal port circuits 110-114 inRFID tag 100. Terminal port circuit 110 c is connected to a terminalport 103 (shown in FIG. 1) of beamforming network 102 (shown in FIG. 1)via terminal port circuit interface 104. Terminal port circuit 110 cincludes a waveguide circuit 115 c and information sources 116 coupledto the waveguide circuit 115 c. For example, waveguide circuit 115 c maybe a microstrip line with couple lines feeding the one or moreinformation sources 116. Alternatively, waveguide circuit 115 c might bea microstrip or stripline power divider that couples power toinformation sources 116. Other variants of waveguide circuit 115 c arepossible.

FIGS. 5 and 6 are schematic illustrations depicting an RFID systemincluding an interrogator and at least one RFID beamforming tag,according to some embodiments. The figures will be described in detailfollowing a preliminary background explanation. FIG. 5 depicts an act orprocess of receiving or reception, in which the interrogator transmitselectromagnetic radiation to the tag, the tag antennas receive thetransmitted electromagnetic radiation, and the tag beamformer directsthe received radiation toward one or more terminal portcircuits/information sources. In this regard, the information source maybe receiving instructions or commands from the interrogator, it may bewriting data to memory on-board the integrated circuit, or it may berectifying the received electromagnetic energy to power the integratedcircuit of the information source. Alternatively, the on-boardintegrated circuit might be in a state that will reflect the receivedpower upon arrival at the on-board integrated circuit. FIG. 6 depicts anact or process of transmission, in which a modulated or encoded form ofthe electromagnetic radiation received from the interrogator istransmitted back to the interrogator by the tag, as described below. Inthe case of a system using RFID tags having integrated circuits, thesignals sent by the interrogator may be continuous wave (CW) signals fora duration of time. The typical response of an RFID tag having anintegrated circuit, when such a CW signal impinges on the RFID tag, willnow be described. Specifically, RFID tags with integrated circuitstypically respond by modulating the CW signal transmitted by theinterrogator, where the modulation is achieved by alternating periods of(1) reflecting the CW signal back to the interrogator and (2) absorbingthe energy of the CW signal. Modulation of the received signal mayinvolve modification not only of its amplitude but also of its phase.During the periods of absorption, less than 100% of the energy may beabsorbed; accordingly, some of the electromagnetic radiation, ordinarilya small portion, may be reflected to the interrogator during the periodsof absorption. In addition, during the periods of absorption,rectification of the absorbed energy may occur, the rectified energybeing used to power and sustain the integrated circuit. In some RFIDprotocols, it is also possible that, during the periods of reflection, asmall amount of power is absorbed to continue supporting the integratedcircuit. FIG. 6 depicts an example of a period (1) during which thereceived signal is being reflected back toward the interrogator (intheory FIG. 6 could also represent period (2) during which the energy ofthe signal is absorbed, assuming the absorption is not 100%, so that aportion of the signal is reflected to the interrogator). In sum, duringperiods (1), namely, reflection, most or all of the power received bythe tag from the interrogator is transmitted back to the interrogator,while during periods (2), namely, absorption, little or none of thepower received by the tag from the interrogator is transmitted back tothe interrogator. It should be noted that reception (shown in FIG. 5)may, and often does, occur simultaneously with transmission (namely,alternating periods of reflection, shown in FIG. 6, and absorption). Theprocess of transmission/modulation varies across different RFIDprotocols. The sequence according to which the tag is alternatelyabsorbing and reflecting power, and the durations of these alternatingprocesses, determine the information with which the signal is modulatedor encoded. In contrast to RFID integrated circuits, other types of RFIDinformation sources, such as SAW circuits, respond by passivelymodulating or encoding the received electromagnetic signal withoutrectification. In SAW-based RFID, signals transmitted by theinterrogator are typically not CW signals, and are often modulated RFpulses. Regardless, the beamforming RFID tag is compatible with the widerange of modulation schemes in practice with both SAW and IC-basedsystems. In the context of a SAW-based RFID system, FIG. 5 representsthe reception of an RF pulse by the beamforming tag, and FIG. 6represents one of a plurality of RF pulses being reflected from the SAWdevice in response to the received pulse. Thus, although FIGS. 5 and 6illustrate distinct processes of receiving and transmittingelectromagnetic power, those of ordinary skill in the art, now havingbenefit of this disclosure, will recognize that the beamforming RFID tagbeamformers and antennas, as passive linear devices, supportsimultaneous reception and transmission of electromagnetic radiation. Tobe sure, the information sources may be capable of exclusive receptionand exclusive transmission.

Turning now to FIG. 5 more closely, RFID interrogator 225 is coupled toa processor 230 and to an antenna 220. RFID interrogator 225 radiates anRFID signal 235, via antenna 220, in the direction of beamforming RFIDtag 202. Tag 202 includes a beamforming network 240, antennas 201coupled to antenna ports 207 of beamforming network 240, and terminalport circuits 231, 232, 233 and 234 coupled respectively to terminalports 203 of beamforming network 240. Each of terminal port circuits231, 232, 233 and 234 includes at least one information source. Eachinformation source includes an RFID source, such as an RFID integratedcircuit or a SAW circuit, and optionally one or more sensors. Asdescribed with respect to FIG. 1, the numbers of antennas 201, antennaports 207, terminal ports 203, and terminal port circuits 231-234 mayvary from that shown in FIGS. 5 and 6.

With continued reference to FIG. 5, RFID signal 235 is received byantennas 201 of tag 202 at an angle 210 a defined relative to Cartesiancoordinate system or frame of reference 214. The RFID signal received bythe antennas 201 is transmitted to the beamforming network 240, and thebeamforming network 240 directs the inputs from the antennas 201 so thatthey add at least substantially in phase at the terminal port(s) 203that correspond(s) to the incident angle 210 a. Thus, the incident RFIDsignal is effectively distributed to a selected one or more of theterminal ports 203, specifically the terminal port(s) 203 correspondingto incident angle 210 a. At each selected terminal port 203, acorresponding one of the terminal port circuits 231-234 receives thepower of the incident signal. (As discussed above with reference to FIG.1, non-selected ones of terminal port(s) 203/terminal port circuits231-234/information sources may receive some signal power, due to thefinite directivity or focusing quality of beamforming networks and/or tounintended scattering, although FIG. 5 does not illustrate signal powerbeing received by non-selected terminal port(s) 203/terminal portcircuits 231-234/information sources.)

In the case illustrated in FIG. 5, the angle 210 a is associated with apeak 211 of the characteristic beam 212 of the beamforming RFID tag. Inthis case, the inputs from the antennas 201 arrive predominantlyin-phase at only one terminal port 203 of the beamforming network 240;as shown in FIG. 5, this terminal port 203 is associated with terminalport circuit 234 having information code ID4. Although only onecharacteristic beam 212 (and hence one peak 211) is shown in FIG. 5, tag202 may have more than one characteristic beam 212, each having a peak211.

FIG. 6 depicts the system (components) of FIG. 5 in a process oftransmission. As mentioned, in the process of reception (FIG. 5), the RFpower added in phase predominantly at one terminal port 203 and enteredthe corresponding terminal port circuit 234. In FIG. 6, terminal portcircuit 234 directs a modulated or encoded form of the received RFenergy back into the beamforming network 240. As discussed above, theprocess of encoding and/or modulating the received signal may result ina substantially reduced or insignificant amount of energy beingtransmitted back to the interrogator during certain finite periods oftime. For information sources comprising RFID integrated circuits,during those periods of time in which a substantially reduced orinsignificant amount of energy is transmitted back to the interrogator,the energy that is not transmitted back but rather absorbed may berectified and used to power the integrated circuit. Due to reciprocityof the beamforming network 240, the antennas 201, and anyinterconnecting waveguides (not shown in FIG. 6), the beamformingnetwork 240 distributes the modulated or encoded signal to the array ofantennas 201 with relative time delays between the respective portionsof the signal reaching successive ones of the antennas 201 such that theresulting transmitted radiation 236 is focused approximately in thedirection of the interrogator 225 (that is, along angle 210 a at whichthe power arrived) or, expressed more simply, such that the signal 236is transmitted back approximately in the direction of the interrogator225.

Although the beamforming RFID tag system is depicted in FIGS. 5 and 6with only a single beam and is described as performing two distinctprocesses for convenience of description, typically the beamforming RFIDtag 202 operates continuously with multiple beams and may perform theprocesses of FIGS. 5 and 6 (reception and transmission) simultaneously.In one or more embodiments, the information sources each comprise adistinct integrated circuit RFID source, such as an RFID integratedcircuit or a SAW circuit, with a unique identification such that eachRFID source is capable of responding to a different interrogator such asprescribed by an RFID protocol standard known as the EPCglobal Class 1Generation 2 UHF standard. For example, an RFID integrated circuitwithin terminal port circuit 234 with identification ID4 is able tocommunicate with an interrogator 225 while simultaneously an RFIDintegrated circuit within terminal port circuit 231 with identificationID1 is able to communicate with a different interrogator (not shown).

In this regard, it should be noted that the orientation of beam 212 is acharacteristic of the device. While in FIGS. 5 and 6, beam 212 isaligned with interrogator 225, if interrogator 225 moves the orientationof beam 212 will not change. Thus, as stated, beamforming RFID tag 202typically operates with multiple beams, as better illustrated, e.g., inFIG. 1. Multiple beams thus permit coverage over a larger continuousangular range than would a single beam, permitting communication betweentag and interrogator while interrogator is within this larger range(discussed also with reference to FIGS. 8 and 9 below).

With continued reference to FIGS. 5 and 6, the shape of the beamformingnetwork depicted therein has the general characteristic outline of aRotman lens with five antenna ports and four terminal ports. However,the choice of five antenna ports and four terminal ports is merely forthe sake of illustration, and as noted, a different number and/orplacement of antenna ports or terminal ports is possible. For example, aterminal port along the center axis of the Rotman lens, as well as twooff-axis points, is often associated with minimal aberration, althoughsuch a central axis terminal port is not shown at this location in FIGS.5 and 6. The number of antenna ports may but is not required to matchthe number of terminal ports. Generally speaking, the Rotman lens has Mantenna elements (antennas) along a linear axis known as an outercontour (not shown in FIGS. 5 and 6) connected to a two-dimensionalpropagation medium, such as parallel plates, by M waveguides that areeach of a specified electrical length. The M waveguides feed thetwo-dimensional propagation medium at antenna ports that lie on aso-called inner contour (not shown in FIGS. 5 and 6) (the M waveguidesconnect the antennas to the antenna ports). The opposing boundary (shownas the “left” side in FIGS. 5 and 6) of the propagation medium is aso-called focal arc, along which N input ports (terminal ports) lie.Each input port is a focal point for radiation traversing thepropagation medium. There are only three optimal points on the focal arcat which the theoretical aberration is zero, but the aberration can bemade acceptably low for many applications. The electrical length of theM waveguides, the x-y coordinates of each antenna port on the innercontour, and the x-y coordinates of each input port on the focal arc areselected such that the radiation arriving from an incident angle (e.g.,210 a in FIG. 5) adds in phase, predominantly, in one region of thefocal arc and is received by one or more input ports in that region. Asshown in FIG. 5, the Rotman lens is configured as an RFIDretro-reflector tag with radiation along the direction associated withID4. As shown, this device constitutes an RFID tag device that issuesfour identification codes, possibly unique, associated with fourdifferent beam positions. If the beams are sufficiently spaced, then itis possible that the device returns only one beam and one associatedidentification. If two or more beams overlap (e.g., as in FIG. 7,described below), it is possible that multiple beams are reflected alongwith the multiple associated identifications. Signal strengthsassociated with each of the beam positions can be used to refine thebearing estimate. In the event that multiple information sources respondto the interrogator, anti-collision mechanisms that prevent interferenceare provided by the RFID protocol medium access control. For example, inmany SAW RFID systems, anti-collision is obtained by using orthogonalcodes for the SAW RFID tags. In many IC-based RFID systems, the tagsrespond in a so-called “aloha” protocol in which only one integratedcircuit responds at any time.

Notwithstanding the general characteristics of the Rotman lens, theintent of FIGS. 5 and 6 is to illustrate a general functionality of thebeamforming RFID tag that is not limited to the selection of anyparticular beamforming network. As stated previously, the selection of agiven beamforming network bestows certain characteristics that might notbe achievable with a different beamforming network. For example, thebeam orthogonality readily achieved with a Butler matrix beamformingnetwork might not be as easily achieved with some Rotman lensbeamforming network implementations.

FIG. 7 is a schematic illustration depicting the system of FIG. 5 but adifferent scenario, in accordance with at least one embodiment. For thesake of convenience in describing this example, FIG. 7 shows twocharacteristic beams 212 and 215, which overlap one another to a smalldegree, rather than the single beam 212 illustrated in FIG. 5. As notedabove, in practice, both the systems shown in FIGS. 5 and 7 wouldtypically operate with multiple beams, which may collectively span alarger continuous angular range. In FIG. 7, the incoming electromagneticradiation or incident signal 236 (also denoted by dashed line 217)arrives at an angle of incidence 210 b (defined with respect toCartesian coordinate system 214), which falls within the edges of thetwo beams 212, 215, in contrast to angle of incidence 210 a that fallsat or near the peak 211 of a single beam 212 as shown in FIG. 5. At thisangle of incidence 210 b, the focal point of the beamforming network 240is nearest to and in between the two terminal ports 203 corresponding toterminal port circuits 233 and 234 and as a result the received powerfrom the antennas 201 adds predominantly in phase at those two terminalports 203. The two terminal port circuits 233 and 234 are thusassociated with characteristic beams 212 and 215, respectively. It willbe understood that although FIG. 7 (like FIG. 5) illustrates a processof reception, a process of transmission (like FIG. 6) also occurs in thesystem of FIG. 7, that is, the information source in each of the twoterminal ports 233, 234 transmits a modulated or encoded form of thereceived signal back into the beamforming network 240 such that therespective modulated or encoded signal is reradiated through therespective one of the characteristic beams 212, 215 associated with therespective terminal port. For example, if (as indicated) characteristicbeam 212 is associated with terminal port circuit 233, a modulated orencoded form of the signal reaching the terminal port circuit 233information source would be reradiated in the direction of beam 212 suchthat power would be returned predominantly in the direction of theinterrogator 225 at an effective antenna gain level as established bythe angle 210 b relative to the peak 211 of beam 212. Similarly, wherecharacteristic beam 215 is associated with terminal port circuit 234, amodulated or encoded form of the signal reaching the terminal portcircuit 234 information source would be reradiated in the direction ofbeam 215 such that power would be returned predominantly in thedirection of the interrogator 225 at an effective antenna gain level asestablished by the angle 210 b relative to the peak 216 of beam 215. Themodulated or encoded signal would be modulated or encoded with theinformation of the one or more RFID sources (such as RFID integratedcircuits or SAW circuits) of the respective terminal port circuit (233or 234) and, in one or more embodiments, with sensor telemetry. Thesignal returned to the interrogator 225 by the beamforming tag 202 isgenerally not in the direction of the peak of the beam unless the angle210 b happens to align with the angle of the beam peak. In general, itis possible that more than two beams will overlap such that aninterrogator will address and communicate with more than two terminalport circuits. As described above, the process of modulating or encodingmay result in a substantially negligible level of power being directedback into the beamforming network over certain delimited periods oftime.

FIG. 8 is a schematic illustration of an RFID system 300 including anRFID beamforming tag 307 attached to one facet 304 of a multi-facetedstructure 301, and multiple interrogators (not illustrated in FIG. 8)mounted on respective mobile platforms 310, 315, in accordance with atleast one embodiment. A first characteristic beam 302 of the tag 307oriented at an upper angle provides a first identification code to afirst mobile platform 310 located at an upper angle relative to thefacet 304 having the tag 307, and a second characteristic beam 305 ofthe tag 307 oriented at a lower angle provides a second identificationcode to a second mobile platform 315 located at a lower angle relativeto the facet 304 having the tag 307. As with FIGS. 5-7, so too in FIG.8, to simplify description of the example, two characteristic beams areshown whereas in practice multiple beams, which may collectively span alarger continuous angular range, would typically be used. In this way,mobile platforms at any angular location relative to the tag within therange may conduct RFID communication with the tag. Also, in someembodiments, multi-faceted structure 301 may have multiple tags 307associated respectively with multiple facets 304. This type of structuremay serve, for example, to further increase the continuous angular rangeof coverage.

FIG. 8 shows the tag transmitting a modulated or encoded signal back tothe interrogator. The reception of the electromagnetic power (sent fromthe interrogator) by the tag is assumed although not shown in FIG. 8.Thus, the modulated signals 303 and 306 shown in FIG. 8 are assumed tobe fully modulated or encoded signals that may be characterized byhaving substantially little or no power over one or more time periodsfor certain types of amplitude modulation. Thus, as seen in FIG. 8,beamforming RFID tag 307 returns two signals 303 and 306 along twodifferent angles associated with characteristic beams 302 and 305,respectively, in response to two interrogation signals (not shown) thatwere previously broadcast by interrogators (not shown) located on thetwo aircrafts (mobile platforms) 310 and 315, respectively, and receivedby the tag 307. The signal 303 with modulated identification broadcastthrough beam 302 is identified by a processor (not shown) coupled to theinterrogator on aircraft 310 as being associated with the specific beam302 belonging to beamforming RFID tag 307. Similarly, a processor (notshown) connected to the interrogator on aircraft 315 receives returnedsignal 306 with modulated identification that was broadcast through beam305 and identifies signal 306 as being associated with beam 305. It isassumed that the position and orientation of beamforming RFID tag 307,as well as the angles associated with each of the beams comprising thecharacteristic beam set of beamforming RFID tag 307, all constituteinformation established a priori and available to each of the processorscoupled to the interrogators on the aircraft 310, 315, respectively, inorder that each of the processors can use the respective receivedmodulated identification to determine the approach angle of therespective aircraft. It is also possible that the aircraft 310, 315receive through wireless communications (not shown) the location andorientation of the constellation of one or more beamforming tags 307(only one shown) from a database or repository (not shown). Thus, basedon one or more signals returned from the constellation of one or morebeamforming tags 307 and on information established and made available apriori to the software program running on the processors, or informationreceived real-time or near-real time through wireless communication, theprocessor is able to determine the approach angle. When the beams withinthe fixed characteristic antenna radiation distribution pattern set of abeamforming RFID tag 307 overlap such that the interrogator in theaircraft receives information from more than one information source (asdescribed with reference to FIG. 7 above), the received signal strengthindication (RSSI) associated with each information source can be used toestimate the angle of incident radiation with greater accuracy and finerresolution. Of course, the processor may also determine range (distance)and range-rate (speed) information, based on the information containedin the returned signal 306 together with the aforementioned informationknown a priori. In addition, it will be understood that just asinformation pertaining to position and orientation of the interrogator(or its platform, aircraft) relative to the tag may be determined by theprocessor, so too information pertaining to position and orientation ofthe tag (or object bearing the tag) relative to the interrogator may bedetermined by the processor, based likewise on the returned signal 306and the aforementioned information known a priori, since the informationpertaining to position and orientation of the tag is equivalent to (forexample, obtainable by simple transformation from) the informationpertaining to position and orientation of the interrogator. (The tag maybe referred to as an entity that transmits a response to electromagneticradiation it receives, e.g., from the interrogator, and the interrogatormay be referred to as an entity that receives the response to theelectromagnetic radiation received by the tag, the response, e.g., beingtransmitted by the tag.) Although FIG. 8 depicts the RFID system 300utilizing beamforming RFID tag 307 as a navigation aid to aircraft 310,315, the concept is directly applicable to navigation aids for othermobile platforms such as automobiles, pedestrians, bicycle riders, etc.equipped with RFID interrogators having connectivity to one or moreprocessors.

FIG. 9 is a schematic illustration of an RFID system 500 including aconstellation of (multiple) beamforming RFID tags 501 and one or moremobile platforms, in accordance with at least one embodiment. Each tag501 has a characteristic beam set 510. Mobile platform(s) may include avehicle 520 or person 530, as illustrated for the sake of this example,or another type of platform, as described above with reference to FIG.8. Each mobile platform is equipped with an interrogator 525(interrogator not shown for person 530). The constellation of tags 501may be used to assist in navigation and/or localization of the mobileplatforms. The term “localization” refers to the determination ofposition and/or orientation of the mobile platform. In some embodiments,the interrogators of mobile platforms 520, 530 are of a type that usesbroad-beam antennas such that signals may be received from multiple (orall) beamforming RFID tags 501 of the constellation. Processors (notshown) coupled to the interrogators use the received signals togetherwith information established a priori such as the position andorientation of each of the beamforming RFID tags 501 to determine theangle of the mobile platform relative to each of the beamforming RFIDtags 501 and, using the determined angles to each of the beamformingRFID tags 501, to determine the position of the mobile platform relativeto the constellation of beamforming RFID tags 501. As part of thisprocess, as described above, the identification information encoded inthe received signal is used to identify the information source andassociated beam from which the signal was received.

With continued reference to FIG. 9, according to a first set ofembodiments the interrogators initiate communication with thebeamforming RFID tags by transmitting an RF signal to the tags, and inresponse the tags transmit return signals to the interrogators. In asecond set of embodiments, the tags are active tags and send signals tothe interrogators (which may be simply receivers) without such priorprompting by the interrogators. In the second set of embodiments, eachof the beamforming RFID tags may include a power source. For example,the terminal port circuit information sources attached to the terminalports of the beamforming RFID tags may be active radios (e.g.,ultra-wideband radios) powered by batteries, the radios transmittingperiodic pulses containing identification information, and theinterrogators may be or include receivers that demodulate and decode theperiodic pulses. In some embodiments of the second set, the radios areattached to sensors and the periodic pulses contain sensor telemetry inaddition to identification information, such that the interrogatorreceivers decode the identification and the sensor telemetry. While theembodiments described in this disclosure with reference to figures otherthan FIG. 9 are for the most part described as operating according tothe first set of embodiments (i.e., two-way communication: tag respondsto signal transmitted by interrogator), it is in general possible toadapt such embodiments to operate according to the second set ofembodiments just described (i.e., one-way communication: tag sendssignal to receiver; receiver does not send signal to tag).

Embodiments operating according to the second set of embodiments (i.e.,one-way communication: tag sends signal to receiver; receiver does notsend signal to tag) may be further characterized as follows. Asdescribed heretofore, the signal (electromagnetic radiation) sent fromtag to receiver may encode one or more identification codes, eachidentification code identifying one of the plurality of informationsources, respectively. The one or more identification codes encoded inthe signal may correspond to angular information indicating an angle atwhich the signal is transmitted. The transmitted signal may, due to theaction of the beamforming network, be distributed to the antennas withthe relative time delay of the signal to each antenna such that thecombined radiation power from the antennas is concentrated within anantenna beam directed over a predetermined angular range according tothe terminal port from which the transmitted signal originated. Thereceiver may be associated with logic configured to derive, from thetransmitted signal (e.g., from the identification codes encodedtherein), information pertaining to a position of the receiver and/or anorientation of the receiver. In this regard, a mapping between theidentification codes of the plurality of information sources and anglesat which the responses are transmitted by the RFID tag may be used. TheRSSI may also be used.

FIG. 10 is a schematic illustration of a beamforming RFID tag 800,wherein the beamforming network 820 is a Butler matrix, in accordancewith at least one embodiment. (As mentioned above, a Butler matrix isdescribed in Phased Array Antennas by A. K. Bhattacharyya (pp.379-415).) beamforming RFID tag 800 includes a Butler matrix beamformingnetwork 820, antennas 861, 862, 863, and 864, each attached to acorresponding antenna port 802 of the beamforming network 820, andterminal port circuits 851, 852, 853, and 854, each attached to acorresponding terminal port 803 of the beam forming network 820. Eachterminal port circuit 851, 852, 853, and 854 includes at least oneinformation source; in some embodiments, each terminal port circuit alsoincludes one or more sensors. In some embodiments, as furtherillustrated in FIG. 10, the Butler matrix beamforming network 820includes hybrid couplers 805 connected to antenna ports 802 on one sideand connected to phase shifters 810 and 811 on the other side, andadditional hybrid couplers 805 connected to phase shifters 810 and 811on one side and to terminal ports 803 on the other side. The formerhybrid couplers 805 (the pair closest to the antennas ports 802) servethe function of power division for incoming signals (signals received bythe tag) and power combining for outgoing signals (signals beingtransmitted from the tag), while the latter hybrid couplers 805 (thepair closest to the terminal ports 803) serve the function of powercombining for incoming signals and power division for outgoing signals.The phase shifters 810 and 811 serve the function of path lengthadjustment for beam steering. All of the hybrid couplers 805 performphase shifting functions in addition to power combining and dividing, asis well known by those of ordinary skill in the art now having benefitof this disclosure. The above-mentioned components of tag 800 areinterconnected, in the manner illustrated in FIG. 10, by RF transmissionlines or waveguides, which may include microstrip line, stripline,synthetic integrated waveguide, or any of numerous other equivalentwaveguiding technologies. Additional meandering of some interconnectinglines, not shown in FIG. 10, may achieve the overall requireddifferences in electrical line lengths. Crossovers 812 indicatetransmission or waveguide lines that permit cross-over of electricalsignals. In an embodiment, this crossover is implemented by wires orvias that cross without established electrical contact. In anotherembodiment, the cross-over is implemented by a microstrip or striplineplanar 4-port cross-over design in which all lines lie within the sameplane such that they can be fabricated on a single printed circuit boardlayer in conjunction with a lower conductive ground plane and anintervening non-conductive substrate layer. See “Microstrip AntennaArray with Four Port Butler Matrix for Switched Beam Base StationApplication” by M. M. Alam (Proceedings of 2009 12^(th) InternationalConference on Computer and Information Technology (ICCIT 2009), 21-23Dec. 2009, Dhaka. Bangladesh, pp. 531-536). The numbers of antennas,antenna ports, terminal port circuits, terminal ports, hybrid couplers,and phase shifters may vary from what is illustrated in FIG. 10.

With continued reference to FIG. 10, in some embodiments the hybridcouplers 805 are branchline hybrid couplers, with the followingcharacteristics. With reference to the hybrid coupler 805 shown at lowerleft in FIG. 10, such a branchline hybrid coupler 805 has a first inputport 830, a second input port 831, a first output port 832, and a secondoutput port 833. The first input port 830 couples power equally to thefirst and second output ports 832 and 833 and the phase of a continuouswave signal at the second output port 833 lags the phase of that at thefirst output port 832 by 90 degrees. Further, the second input port 831is theoretically isolated from the first input port 830 such that nopower theoretically reaches the second input port 831 from the firstinput port 830 except that portion which reflects from the first outputport 832 or the second output port 833 and returns to the second inputport 831. Assuming the other three hybrid couplers 805 shown in FIG. 10are similarly constructed with (as illustrated) the lower left side portrepresenting the first input port, the lower right side portrepresenting the second input port, the upper left side portrepresenting the first output port, and the upper right side portrepresenting the second output port, and further assuming that phaseshifters 810 and 811 each represent a 45 degree phase delay at thecenter frequency of operation, then the signal phase progression at thecenter frequency of operation and normalized to 0 degrees at antenna861, for an input source at the place of terminal port circuit 851,would be 0 degrees at antenna 861, −45 degrees at antenna 862, −90degrees at antenna 863, and −135 degrees at antenna 864. Such a phaseprogression would produce a steered beam, the angle of the steered beambeing dependent upon the frequency of operation and the spacing betweenantennas 861-864. Considering the same example with the source at theplace of terminal port circuit 852 instead of 851, the phase progressionacross the antennas 861-864 from left (antenna 861) to right (antenna864) would be in increments of +135 degrees. For the source locatedinstead at the place of terminal port circuit 853, the phase progressionwould be in increments of −135 degrees, and for the source locatedinstead at the place of terminal port circuit 854, the phase progressionwould be in increments of +45 degrees. The angle theta to which the beamis steered is given by sin(theta)=psi/(kd), where d is the linearseparation space between the apparent or effective phase centers ofadjacent antennas, psi is the phase progression, k=omega/c, omega is theradian frequency, and c is the speed of light. It should be noted thatthis embodiment is just one example of a Butler matrix implementation,and many other implementations of the Butler matrix or of derivatives ofthe Butler matrix are possible and could be used in the design anddevelopment of a beamforming RFID tag.

FIG. 11 is a schematic illustration of a Rotman lens beamforming network900 for a microstrip type implementation, in accordance with at leastone embodiment described herein. The Rotman lens beamforming network 900includes a plurality of antenna ports 901, a plurality of terminal ports913, and a plurality of dummy ports 910. Dummy ports 910 are oftenplaced along regions of the focal arc that lie outside of the designregion in which focusing can be obtained, yet still may receiveradiation outside of the design intent, often due to the broaddistribution of electromagnetic power from an antenna port or a terminalport. In typical applications of Rotman lenses, loaded dummy ports areoften placed along these extensions of the focal arc in order that theimpinging scattered radiation not reflect and subsequently degrade thesignal radiating toward either the antennas or the terminal ports. Thenumbers of antenna ports 901, terminal ports 913, and dummy ports 910may differ from what is illustrated in FIG. 11. Typically, such amicrostrip type Rotman lens would include a layer of conductive materialthat resides on top of an insulating region, and the opposing side ofthe insulating region would include a ground plane. The outline of theshape shown in FIG. 11 represents the outer boundary of the layer ofconductive material. Signals received by antennas (not shown) connectedto antenna ports 901 propagate through a parallel plate region formed bythe layer of conductive material and the ground plane beneath it, andadd in phase at a region around a subset of the terminal ports 913, theconfiguration of this region depending on the specific design of theRotman lens contours and the angle of arrival of the incident signals.In some embodiments, terminal port circuits (not shown) attached to theterminal ports 913 of the Rotman beamforming network 900 receive thefocused energy and the terminal port circuit information sources directa modulated or encoded form of the received signal back into the Rotmanbeamforming network 900 such that the resulting signal is sent back inthe direction of the interrogator (not shown) to the extent that theangle to the interrogator relative to the beamformer antenna array iswithin one or more of the characteristic beams of the beamforming RFIDtag. In other embodiments, each terminal port circuit is or includes aradio that periodically broadcasts a signal including an identificationcode or information unique to that terminal port circuit, and the signalis received by an interrogator that may be simply a receiver; noinitiating signal from interrogator to tag is required. In some of theseembodiments, the radios are ultra-wideband (UWB) radios. In someembodiments, telemetry from one or more sensors (in the terminal portcircuits) is also transmitted by each terminal port circuit.

FIG. 12 is a schematic illustration of a multi-faceted beamforming RFIDtag 1000, in accordance with at least one embodiment. Multi-facetedbeamforming RFID tag 1000 includes a multi-faceted structure 1002including three utilized faces 1003 and one unutilized face 1005. Eachutilized face 1003 includes an antenna, antenna port, terminal port (theantenna, antenna port, and terminal port are not specifically shown inFIG. 12 but have been described and illustrated generally in otherfigures herein, such as the antenna 101, the antenna port 107, and theterminal port 103 of FIG. 1), and terminal port circuit 1004, eachterminal port circuit 1004 including an information source which may bean RFID source, such as an RFID integrated circuit or a SAW circuit.These components are interconnected, as has been described withreference to other illustrated embodiments herein. The unutilized face1005 is not utilized for RFID. Each antenna may have a single fixedbeam, such that the tag 1000 has a characteristic set of beams 1010,1011, and 1012 that cover a region of space through which thebeamforming RFID tag 1000 is capable of communicating with one or moreinterrogators (not shown) in different directions. While tag 1000 doesnot have a beamforming network per se, the functional equivalent ofbeamforming is implemented by the arrangement of the single beamantennas on the multi-faceted structure. In some embodiments, theterminal port circuits 1004 include sensors in addition to the RFIDsources. In some embodiments, the beams 1010, 1011, and 1012 of thecharacteristic antenna radiation distribution pattern set overlap tosome extent so as to provide for communication over a continuous angularrange, as described above with respect to other illustrated embodiments.In some embodiments, each of the beams 1010, 1011, and 1012 receivesincident radiation that is then coupled to the corresponding informationsource, which encodes the received signal with identificationinformation and, if applicable, sensor telemetry information prior toretransmitting the signal back through the corresponding antenna. Inother embodiments, each terminal port circuit 1004 is or includes aradio that periodically transmits an RF signal modulated withidentification information and, in applicable embodiments, sensortelemetry information, to be received by an interrogator or in otherembodiments by a receiver; in these embodiments of one-waycommunication, transmission of an incident signal from an interrogatorto the tag 1000 is not required. In some of these embodiments, theradios are ultra-wideband radios. The number of facets, the number ofutilized facets 1003 and unutilized facets 1005, and the numbers of thecomponents associated with each utilized facet 1003 may differ from whatis illustrated in FIG. 12. The number, spacing, and direction of beams1010, 1011 and 1012 may also differ from what is illustrated in FIG. 12.

FIG. 13 is a schematic illustration of a multi-faceted beamforming RFIDtag 1100, in accordance with at least one embodiment. Multi-facetedbeamforming RFID tag 1100 includes a multi-faceted structure 1102including three utilized faces 1103 and one unutilized face 1105. Theunutilized face 1105 is not utilized for RFID. Each utilized face 1103has a (single-facet) beamforming RFID tag (not shown as such) thatincludes a beamforming network (not shown), antennas (not shown) eachconnected to a respective antenna port (not shown), and three terminalport circuits 1104 each connected to a terminal port (not shown), eachterminal port circuit 1104 including an information source which may bean RFID source (such as an RFID integrated circuit or a SAW circuit),and, optionally, one or more sensors. (While each utilized face 1103 isshown as having a characteristic beam set 1101 of three beams, thenumber of antennas need not be the same as the number of beams.) Thesecomponents are interconnected, as has been described with reference toother illustrated embodiments herein. Each single-facet beamforming RFIDtag has a characteristic beam set 1101 that provides coverage over adefined angular region, and each of the beams of the characteristic beamset 1101 is associated with one or more terminal ports of thebeamforming network. The combined coverage provided by the threesingle-facet beamforming RFID tags is greater than the coverage providedby any single one of the single-facet beamforming RFID tags. Beamformingnetworks and attached antennas on planar structures are limited withrespect to the angular communication coverage provided. Themulti-faceted beamforming RFID tag 1100 overcomes or mitigates thislimitation because it includes multiple beamforming RFID tags disposedon different facets (planar surfaces), respectively, of multi-facetedbeamforming RFID tag 1100, which collectively provide characteristicbeams over a larger angular region than does any single one of thesingle-facet beamforming tags. A multi-faceted beamforming RFID tag mayalso provide increased coverage compared to an enlarged size singlefacet (planar array) tag due to the fact that achievable gain is at amaximum broadside to the planar array and falls off as the position ofthe signal moves toward the edges of the array. In some embodiments, theterminal port circuits 1104 of the single-facet beamforming RFID tagsare or include RFID integrated-circuits that respond to an interrogator(not shown) by backscattering a signal transmitted by the interrogator.In some embodiments, the terminal port circuits 1104 of the single-facetbeamforming RFID tags are or include SAW RFID circuits.

As with the tag 1000 of FIG. 12, the tag 1100 of FIG. 13 may becharacterized by the following features. The beams of the characteristicantenna radiation distribution pattern sets 1101 may overlap to someextent so as to provide for communication over a continuous angularrange, as described above with respect to other illustrated embodiments.The tag 1100 may receive incident radiation from an interrogator andtransmit a modulated form of the received signal back to theinterrogator, the modulated signal including identification informationand, if applicable, sensor telemetry information. Alternatively, the tag1100 may include in terminal port circuit 1104 a radio (e.g.,ultra-wideband radio) that periodically transmits a modulated RF signalto an interrogator (receiver), without prompting by an incident signalfrom the interrogator. The number of facets, the number of utilizedfacets 1103 and unutilized facets 1105, and the numbers of thecomponents and beams associated with each utilized facet 1103 may differfrom what is illustrated in FIG. 13. The number, spacing, and directionof beams 1101 may also differ from what is illustrated in FIG. 13.

In the case of multi-faceted beamforming RFID tag 1100, described abovewith reference to FIG. 13, the beamforming network may be, among otherthings, a microwave lens, a Rotman lens, a Butler matrix, a Blassmatrix, or formed of power dividers and combiners, all of which havebeen described above. Again, multi-faceted beamforming RFID tag 1100 mayinclude a power combining network for each face to which antennas areattached. The terminal port circuits may be attached to the terminalports of the power combining network. The power combining circuit ofeach face may couple the one or more antennas on the face so thatsignals received by the antennas from an RFID interrogator add at asingle terminal port of the face and, reciprocally, signals transmittedat the single terminal port of the face are distributed to the face'santennas connected to the power combining circuit for radiating back toan RFID interrogator, wherein the multiple faces to which antennas areattached are oriented with respect to each other to provide antennacoverage over the desired angular region. Each of the one or more facesmay provide coverage over a fixed predefined angular region. As comparedto conventional omnidirectional tags, the faces of multi-faceted tagsmay provide increased directivity, whereby interrogation range (linearextent of RFID communication) may be increased. Resolution and accuracyof angular measurement of interrogator (mobile platform) may beincreased by narrowing the beamwidth of the constituent faces (increasedaperture size) and consequently increasing the number of faces utilized.In addition to the various types of beamforming networks describedabove, van Atta retro-reflectors (described below with reference to FIG.16) may be used in multi-faceted beamforming RFID tags. In sum,multi-faceted beamforming RFID tags may provide increased spatialcoverage (angular extent of coverage), directivity, range (linear extentor maximum distance within which communication can be conducted), andresolution.

FIG. 14 is a schematic diagram illustrating an exemplary spatial rangeof coverage of two single facet beamforming RFID tags, in accordancewith at least one embodiment. Each of two beamforming RFID tags 1202 aand 1202 b has a characteristic set of antenna radiation distributionpatterns (beams) that provides coverage over a defined angular region,as described above. As shown in the figure, that angular region, orangular range of coverage, of beamforming tags 1202 a and 1202 b, isrepresented by angles 1208 a (CAB) and 1208 b (FDE), respectively, whichsubtend sides BC and EF of triangles ABC and DEF, respectively, whichare the longest sides of those triangles. Triangles ABC and DEF may besaid to represent the partitioning of space by the two tags 1202 a and1202 b. In other embodiments, the range of coverage, and the magnitudesof angles 1208 a and 1208 b, may vary from what is illustrated in FIG.14, e.g., due to change of the characteristic beam set or change inother aspect(s) of the arrangement. Of course, other arrangements havingdifferent numbers of tags may also be provided.

FIG. 15 is a schematic diagram illustrating an exemplary spatial rangeof coverage of two multi-faceted beamforming RFID tags, in accordancewith at least one embodiment. Each of two multi-faceted beamforming RFIDtags 1300 a and 1300 b includes a multi-faceted structure 1302 a and1302 b, respectively. Multi-faceted structure 1302 a has two utilizedfaces 1303 a-i and 1303 a-ii and three unutilized faces 1305 a, andmulti-faceted structure 1302 b has two utilized faces 1303 b-i and 1303b-ii and three unutilized faces 1305 b. Each of the utilized faces 1303a-i, 1303 a-ii, 1303 b-i, and 1303 b-ii has a beamforming RFID tag (notshown as such). Each beamforming RFID tag has a characteristic set ofantenna radiation distribution patterns (beams) that provides coverageover a defined angular region, as described above. As shown in thefigure, that angular region, or angular range of coverage, of thebeamforming tags on utilized faces 1303 a-i, 1303 a-ii, 1303 b-i, and1303 b-ii, is represented by angles 1308 a-i (IGH), 1308 a-ii (UK), 1308b-i (NMO), and 1308 b-ii (QPR), respectively, which subtend sides HI,KL, NO, and QR of triangles GHI, JKL, MNO and PQR, respectively, whichare the longest sides of those triangles. Triangles GHI, JKL, MNO andPQR may be said to represent the partitioning of space by the four tagsof the four utilized faces 1303 a-i, 1303 a-ii, 1303 b-i, and 1303 b-ii,respectively. To be sure, the dotted portions of triangles JKL and MNOdo not represent portions of the range of coverage of tags 1300 a and1300 b, respectively, as each of these regions is blocked by the othertag (1300 b and 1300 a, respectively). In other embodiments, the rangeof coverage, and the magnitudes of angles 1308 a-i, 1308 a-ii, 1308 b-i,and 1308 b-ii, may vary from what is illustrated in FIG. 15, e.g., dueto change of the characteristic beam set or change in other aspect(s) ofthe arrangement. Of course, other arrangements having different numbersof tags or utilized faces may also be provided.

FIG. 16 is a schematic diagram illustrating a hybrid Rotman lens/vanAtta retro-reflector, in accordance with at least one embodiment. Thehybrid Rotman lens/van Atta retro-reflector is a hybrid combination of aRotman lens, as described above, and a van Atta retro-reflector, asdescribed in U.S. Pat. No. 8,466,776, issued on Jun. 18, 2013, which ishereby incorporated herein in its entirety. The hybrid Rotman lens/vanAtta retro-reflector is formed by connecting corresponding input ports(terminal ports) on pairs of Rotman lenses as van Atta pairs. As seen inFIG. 16, two Rotman lenses 1400 a and 1400 b are provided, each oneconnected to a set of antennas 1401 a and 1401 b, respectively, and to aset of input ports 1403 a and 1403 b, respectively. Input ports 1403 aare connected to corresponding ones of input ports 1403 b, respectively.RFID functionality can be incorporated in this arrangement as describedin aforementioned U.S. Pat. No. 8,466,776. This arrangement can bescaled by adding additional van Atta pairs of Rotman lenses. The hybridRotman lens/van Atta retro-reflector provides full steering over twoorthogonal angles.

FIG. 417 is a flow chart illustrating a method of RFID 1500 using one ormore beamforming RFID tags. Each beamforming RFID tag includes aplurality of information sources and a beamforming network. At step1505, electromagnetic radiation (e.g., an RFID signal) is transmitted.This signal may be transmitted by an interrogator and may be intended tobe received by an RFID beamforming tag. At step 1510, the transmittedsignal is received, e.g., by the tag via antennas of the tag. The signalmay be received at an angle of incidence relative to a fixed coordinatesystem and through one or more characteristic beams of the set ofcharacteristic beams implemented by the beamforming network inconjunction with the antennas. At step 1515, the received signal isdirected, e.g., by the beamforming network of the tag, to a subset ofthe plurality of information sources within the tag. Such subset may butneed not include all of the information sources of the tag. The subsetof the plurality of information sources to which the received signal isdirected may be determined based on the angle of incidence. At step1525, an encoded response (signal) to the received signal istransmitted. The response is encoded with (a) identification codes ofthe subset of the plurality of information sources to which the receivedsignal was directed and, optionally, (b) sensor telemetry. The responsemay thus be based on the subset of the plurality of information sourcesto which the received signal was directed. The response may betransmitted to the interrogator. The response may be transmitted (a) atthe angle of incidence (the angle at which the signal was received) and(b) in a direction opposite to the direction from which the signal wasreceived. The response may be transmitted through the one or morecharacteristic beams through which the received signal was received instep 1510. The received signal may be used as a source of power fortransmitting the response. At step 1530, the response is received, e.g.by the interrogator. At step 1535, information pertaining to a positionor an orientation of an entity that received the response (e.g., theinterrogator), relative to an entity that transmitted the response(e.g., the tag), or information pertaining to a position or anorientation of an entity that transmitted the response (e.g., the tag),relative to an entity that received the response (e.g., theinterrogator), is derived, based on the received response, a mappingbetween the identification codes and the angles of signal transmission,and the RSSI. Such position (or ranging) information may include, e.g.,a(n estimated) distance from the interrogator (or mobile platformhousing the interrogator) to the tag (or object bearing the tag), or a(nestimated) location of the interrogator/platform or tag/object. Thedistance may be determined (estimated) based on the elapsed time betweenthe transmission of the signal by the interrogator and the reception ofthe response signal from the tag. Such position information may be usedfor navigation, localization and/or tracking of the mobile platformhousing the interrogator or of the object bearing the tag. Suchorientation (or angular) information may include, e.g., a(n estimated)bearing (angle) of the interrogator (or mobile platform housing theinterrogator) relative to the tag (or object bearing the tag), or of thetag relative to the interrogator. Such orientation information may beused for navigation, localization and/or tracking of the mobile platformhousing the interrogator or of the object bearing the tag. Followingstep 1535, one or more additional responses to one or more additionalreceived signals, respectively, may be received, e.g., by theinterrogator, and the initial response may be compared to the one ormore additional responses. Such comparison may facilitate or improvenavigation, localization and/or tracking of the mobile platform housingthe interrogator or of the object bearing the tag. It will be notedthat, while an initial instance of step 1525 (transmission of response)must be preceded by an instance of step 1510 (reception of incomingelectromagnetic radiation) and an instance of step 1515 (directing ofreceived incoming electromagnetic radiation to information source(s)),otherwise the steps of method 1500 and the other steps mentioned in thisparagraph may occur in temporal sequence(s) other than that illustratedin FIG. 17 and described in this paragraph. For example, step 1510and/or step 1515 may occur concurrently with step 1525.

FIG. 18 is a flow chart illustrating a method of RFID 1600 using one ormore beamforming RFID tags. Each beamforming RFID tag includes aplurality of information sources and a beamforming network. At step1625, encoded electromagnetic radiation (e.g., an encoded RF signal) istransmitted. The signal is encoded with (a) one or more identificationcodes, each of the identification codes identifying a respective one ofthe plurality of information sources of the tag and, optionally, (b)sensor telemetry. The one or more identification codes with which thesignal is encoded may correspond to angular information indicating anangle at which the signal is transmitted. The signal may be transmittedto a receiver. At step 1630, the signal is received, e.g. by thereceiver. At step 1635, information pertaining to a position or anorientation of an entity that received the signal (e.g., the receiver),relative to an entity that transmitted the signal (e.g., the tag), orinformation pertaining to a position or an orientation of an entity thattransmitted the signal (e.g., the tag), relative to an entity thatreceived the signal (e.g., the receiver), is derived (e.g., by logicassociated with the receiver), based on the transmitted signal, amapping between the identification codes and the angles of signaltransmission, and the RSSI. Such position (or ranging) information mayinclude, e.g., a(n estimated) distance from the receiver (or mobileplatform housing the receiver) to the tag (or object bearing the tag),or a(n estimated) location of the receiver/platform or tag/object. Thedistance may be determined (estimated) based on the elapsed time betweenthe transmission of the signal by the tag and the reception of thesignal by the receiver. Such position information may be used fornavigation, localization and/or tracking of the mobile platform housingthe receiver or of the object bearing the tag. Such orientation (orangular) information may include, e.g., a(n estimated) bearing (angle)of the receiver (or mobile platform housing the receiver) relative tothe tag (or object bearing the tag), or of the tag relative to thereceiver. Such orientation information may be used for navigation,localization and/or tracking of the mobile platform housing the receiveror of the object bearing the tag. Following step 1635, one or moreadditional signals may be received, e.g., by the receiver, and theinitial signal may be compared to the one or more additional signals.Such comparison may facilitate or improve navigation, localizationand/or tracking of the mobile platform housing the receiver or of theobject bearing the tag.

In light of the principles and exemplary embodiments described andillustrated herein, it will be recognized that the exemplary embodimentscan be modified in arrangement and detail without departing from suchprinciples. Also, the foregoing discussion has focused on particularembodiments, but other configurations are contemplated. In particular,even though expressions such as “in one embodiment,” “in anotherembodiment,” “in a version of the embodiment” or the like are usedherein, these phrases are meant to generally reference the range ofpossibilities of embodiments, and are not intended to limit thedisclosure to the particular embodiments and configurations describedherein. As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments.

Similarly, although exemplary processes have been described with regardto particular operations performed in a particular sequence, numerousmodifications could be applied to those processes to derive numerousalternative embodiments of the present disclosure. For example,alternative embodiments may include processes that use fewer than all ofthe disclosed operations, processes that use additional operations, andprocesses in which the individual operations disclosed herein arecombined, subdivided, rearranged, or otherwise altered.

In view of the wide variety of useful permutations that may be readilyderived from the exemplary embodiments described herein, this detaileddescription is intended to be illustrative only, and should not be takenas limiting the scope of the disclosure. What is claimed as thedisclosure, therefore, are all implementations that come within thescope of the following claims, and all equivalents to suchimplementations. In the claims, means-plus-function andstep-plus-function clauses are intended to cover the structures or actsdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, while anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures.

What is claimed is:
 1. A radio frequency identification (RFID) system,comprising: an RFID tag comprising: a plurality of information sources;and a beamforming network, wherein the RFID tag is configured to receiveelectromagnetic radiation from an RFID interrogator, the beamformingnetwork is configured to direct the received electromagnetic radiationto a subset of the plurality of information sources, and the RFID tag isconfigured to transmit a response to the received electromagneticradiation, the response based on the subset of the plurality ofinformation sources to which the received electromagnetic radiation wasdirected.
 2. The system of claim 1, wherein the RFID tag furthercomprises a plurality of antennas, the RFID tag being configured toreceive the electromagnetic radiation via the plurality of antennas, andwherein the beamforming network and antennas produce a plurality ofantenna radiation distribution patterns, each antenna radiationdistribution pattern being associated with a respective one or more ofthe information sources.
 3. The system of claim 1, wherein the RFID tagis further configured to receive the electromagnetic radiation at anangle of incidence relative to a fixed coordinate system at the tag, andthe beamforming network is configured to direct the receivedelectromagnetic radiation to the subset of the plurality of informationsources based on the angle of incidence.
 4. The system of claim 1,wherein the RFID tag is further configured to transmit the response tothe received electromagnetic radiation (a) at an angle of incidencerelative to a fixed coordinate system, the angle of incidence being anangle at which the electromagnetic radiation was received, and (b) in adirection opposite to a direction from which the electromagneticradiation was received.
 5. The system of claim 1, wherein the RFID tagcomprises a plurality of faces, each face comprising one or moreantennas and being associated with one or more of the informationsources and a portion of the beamforming network.
 6. The system of claim1, wherein each information source comprises at least one of thefollowing: an integrated circuit, a surface acoustic wave circuit, or asensor.
 7. The system of claim 1, wherein the beamforming networkcomprises one of the following: a microwave lens; a Rotman lens; a Ghentlens; a Luneberg lens; a Butler matrix; a Blass matrix; a combination ofpower combiners, power dividers, waveguides, and phase shifters; acombination of hybrid couplers, waveguides, and phase shifters; or aderivative of one of the preceding.
 8. The system of claim 1, furthercomprising: said RFID interrogator configured to transmit theelectromagnetic radiation to the RFID tag and to receive the response tothe electromagnetic radiation.
 9. The system of claim 8, furthercomprising a mobile platform housing the interrogator.
 10. The system ofclaim 8, wherein the interrogator is associated with logic configured toderive, from the response, information pertaining to one or more of thefollowing: a position of the interrogator, and an orientation of theinterrogator.
 11. The system of claim 8, wherein each of the informationsources includes an identification code, the response is encoded withthe identification codes of the subset of the plurality of informationsources to which the received electromagnetic radiation was directed,and the interrogator is associated with a mapping between theidentification codes of the plurality of information sources and anglesat which the responses are transmitted by the RFID tag.
 12. A radiofrequency identification (RFID) method, comprising: receivingelectromagnetic radiation from an RFID interrogator; directing thereceived electromagnetic radiation to a subset of a plurality ofinformation sources via a beamforming network within an RFID tag; andtransmitting a response to the received electromagnetic radiation,wherein the response is based on the subset of the plurality ofinformation sources to which the received electromagnetic radiation wasdirected.
 13. The method of claim 12, wherein the electromagneticradiation is received at an angle of incidence relative to a fixedcoordinate system, and the subset of the plurality of informationsources to which the received electromagnetic radiation is directed isdetermined based on the angle of incidence.
 14. The method of claim 12,wherein the response to the received electromagnetic radiation istransmitted (a) at an angle of incidence relative to a fixed coordinatesystem, the angle of incidence being an angle at which theelectromagnetic radiation was received, and (b) in a direction oppositeto a direction from which the electromagnetic radiation was received.15. The method of claim 12, wherein the response to the receivedelectromagnetic radiation is encoded with the identification codes ofthe subset of the plurality of information sources to which the receivedelectromagnetic radiation was directed.
 16. The method of claim 12,further comprising: transmitting the electromagnetic radiation from anRFID interrogator; and receiving the response to the receivedelectromagnetic radiation from the RFID tag.
 17. The method of claim 16,further comprising deriving, based on the received response to thereceived electromagnetic radiation, information pertaining to a positionor an orientation of an entity that received the response to thereceived electromagnetic radiation, relative to an entity thattransmitted the response to the received electromagnetic radiation, orof an entity that transmitted the response to the receivedelectromagnetic radiation, relative to an entity that received theresponse to the received electromagnetic radiation.
 18. A radiofrequency identification (RFID) system, comprising; an RFID tagcomprising: a plurality of information sources; and a passivebeamforming network, wherein the RFID tag is configured to receiveelectromagnetic radiation from an RFID interrogator, the beamformingnetwork is configured to direct the received electromagnetic radiationto a subset of the plurality of information sources, and the RFID tag isconfigured to transmit a response to the received electromagneticradiation, the response based on the subset of the plurality ofinformation sources to which the received electromagnetic radiation wasdirected.
 19. The system of claim 18, wherein the RFID tag furthercomprises a plurality of antennas, the RFID tag being configured toreceive the electromagnetic radiation via the plurality of antennas, andwherein the passive beamforming network and antennas produce a pluralityof antenna radiation distribution patterns, each antenna radiationdistribution pattern being associated with a respective one or more ofthe information sources.
 20. The system of claim 18, wherein the RFIDtag is further configured to receive the electromagnetic radiation at anangle of incidence relative to a fixed coordinate system at the RFIDtag, and the passive beamforming network is configured to direct thereceived electromagnetic radiation to the subset of the plurality ofinformation sources based on the angle of incidence.
 21. The system ofclaim 18, wherein the RFID tag is further configured to transmit theresponse to the received electromagnetic radiation (a) at an angle ofincidence relative to a fixed coordinate system, the angle of incidencebeing an angle at which the electromagnetic radiation was received, and(b) in a direction opposite to a direction from which theelectromagnetic radiation was received.
 22. The system of claim 18,further comprising: said RFID interrogator configured to transmit theelectromagnetic radiation to the RFID tag and to receive the-response tothe electromagnetic radiation from the RFID tag wherein the interrogatoris associated with logic configured to derive, from the response of theRFID tag, information pertaining to one or more of the following; aposition of the interrogator, and an orientation of the interrogator.